Reducing location-dependent interference in distributed antenna systems operating in multiple-input, multiple-output (MIMO) configuration, and related components, systems, and methods

ABSTRACT

Components, systems, and methods for reducing location-based interference in distributed antenna systems operating in multiple-input, multiple-output (MIMO) configuration are disclosed. Interference is defined as issues with received MIMO communications signals that can cause a MIMO algorithm to not be able to solve a channel matrix for MIMO communications signals received by MIMO receivers in client devices. These issues may be caused by lack of spatial (i.e., phase) separation in the received MIMO communications signals. Thus, to provide phase separation of received MIMO communication signals, multiple MIMO transmitters are each configured to employ multiple transmitter antennas, which are each configured to transmit in different polarization states. In certain embodiments, one of the MIMO communications signals is phase shifted in one of the polarization states to provide phase separation between received MIMO communication signals. In other embodiments, multiple transmitter antennas in a MIMO transmitter can be offset to provide phase separation.

PRIORITY APPLICATION

This application is a continuation of International Application No.PCT/US13/034,328 filed on Mar. 28, 2013, which claims priority to U.S.Provisional Patent Application No. 61/618,396 filed on Mar. 30, 2012,both of which are relied upon and incorporated herein by reference intheir entirety.

RELATED APPLICATION

This application is related to U.S. Provisional Patent Application No.61/541,566 entitled “AUTOMATIC ANTENNA SELECTION BASED ON ORIENTATION,AND RELATED APPARATUSES, ANTENNA UNITS, METHODS, AND DISTRIBUTED ANTENNASYSTEMS,” filed on Sep. 30, 2011, which is incorporated herein byreference in its entirety.

BACKGROUND

1. Field of the Disclosure

The technology of the disclosure relates to distribution of data (e.g.,digital data services and radio-frequency communications services) in adistributed antenna system.

2. Technical Background

Wireless customers are demanding digital data services, such asstreaming video signals. Concurrently, some wireless customers use theirwireless devices in areas that are poorly served by conventionalcellular networks, such as inside certain buildings or areas where thereis little cellular coverage. One response to the intersection of thesetwo concerns has been the use of distributed antenna systems.Distributed antenna systems can be particularly useful to be deployedinside buildings or other indoor environments where client devices maynot otherwise be able to effectively receive radio-frequency (RF)signals from a source. Distributed antenna systems include remote units(also referred to as “remote antenna units”) configured to receive andwirelessly transmit wireless communications signals to client devices inantenna range of the remote units. Such distributed antenna systems mayuse Wireless Fidelity (WiFi) or wireless local area networks (WLANs), asexamples, to provide digital data services.

Distributed antenna systems may employ optical fiber to supportdistribution of high bandwidth data (e.g., video data) with low loss.Even so, WiFi and WLAN-based technology may not be able to providesufficient bandwidth for expected demand, especially as high definition(HD) video becomes more prevalent. WiFi was initially limited in datarate transfer to 12.24 Mb/s and is provided at data transfer rates of upto 54 Mb/s using WLAN frequencies of 2.4 GHz and 5.8 GHz. Whileinteresting for many applications, WiFi bandwidth may be too small tosupport real time downloading of uncompressed high definition (HD)television signals to wireless client devices.

Multiple-input, multiple-output (MIMO) technology can be employed indistributed antenna systems to increase the bandwidth up to twice thenominal bandwidth, as a non-limiting example. MIMO is the use ofmultiple antennas at both a transmitter and receiver to increase datathroughput and link range without additional bandwidth or increasedtransmit power. However, even doubling bandwidth alone may not be enoughto support high bandwidth data to wireless client devices, such as theexample of real time downloading of uncompressed high definition (HD)television signals.

The frequency of wireless communications signals could also be increasedin a MIMO distributed antenna system to provide larger channel bandwidthas a non-limiting example. For example, an extremely high frequency(EHF) in the range of approximately 30 GHz to approximately 300 GHzcould be employed. For example, the sixty GHz (60 GHz) spectrum is anEHF that is an unlicensed spectrum by the Federal CommunicationsCommission (FCC). EHFs could be employed to provide for larger channelbandwidths. However, higher frequency wireless signals are more easilyattenuated and/or blocked from traveling through walls, buildingstructures, or other obstacles where distributed antenna systems arecommonly installed. Higher frequency wireless signals also providenarrow radiation patterns. Thus, remote units in distributed antennasystems may be arranged for line-of-sight (LOS) communications to allowfor higher frequencies for higher bandwidth. However, if remote unitsare provided in a LOS configuration, and the remote units are alsoconfigured to support MIMO, multiple data streams in the same frequencychannel will be received by multiple receiver antennas in the remoteunits. This can lead to multiple data streams received in the samefrequency channel leading to performance degradation and limitedwireless coverage where the MIMO algorithm can fail to solve the channelmatrix.

SUMMARY OF THE DETAILED DESCRIPTION

Components, systems, and methods for reducing location-basedinterference in distributed antenna systems operating in multiple-input,multiple-output (MIMO) configuration are disclosed. The distributedantenna systems include remote units employing MIMO transmittersconfigured to transmit multiple data streams in MIMO configuration toMIMO receivers in wireless client devices. Interference is defined asissues with received MIMO communications signals that can cause a MIMOalgorithm to not be able to solve a channel matrix for MIMOcommunications signals received by MIMO receivers in client devices.These issues can occur due to lack of spatial (i.e., phase) separationin the received MIMO communications signals, especially with closelylocated MIMO transmitters configured for line-of-sight (LOS)communications. Thus, to provide phase separation of MIMO communicationsignals received by MIMO receivers in client devices, multiple MIMOtransmitters in a remote unit are each configured to employ multipletransmitter antennas, which are each configured to transmit in differentpolarization states. In certain embodiments, one of the MIMOcommunications signals is phase shifted in one of the polarizationstates to provide phase separation between MIMO communication signalsreceived by the MIMO receivers. In other embodiments, multipletransmitter antennas in a MIMO transmitter can be offset to providephase separation.

The components, systems, and methods for location-based interference ina distributed antenna systems operating in MIMO configuration maysignificantly improve high-data rate wireless coverage withoutsignificant dependence on transmitter and/or receive placement. This mayallow for LOS communications to be more easily achieved, especially forhigher frequency communications where LOS communications may be employedto reduce the effect of obstacles. High antenna isolation is notrequired in the MIMO receivers. The increased coverage area can alsoallow for higher efficiency at higher frequencies typically inefficientfor radio frequency (RF) amplifiers.

In this regard, in one embodiment, a MIMO remote unit configured towirelessly distribute MIMO communications signals to wireless clientdevices in a distributed antenna system is provided. The MIMO remoteunit comprises a first MIMO transmitter comprising a first MIMOtransmitter antenna configured to transmit MIMO communications signalsin a first polarization and a second MIMO transmitter antenna configuredto transmit MIMO communications signals in a second polarizationdifferent from the first polarization. The MIMO remote unit alsocomprises a second MIMO transmitter comprising a third MIMO transmitterantenna configured to transmit MIMO communications signals in the firstpolarization and a fourth MIMO transmitter antenna configured totransmit MIMO communications signals in the second polarization. Thefirst MIMO transmitter is configured to receive a first downlink MIMOcommunications signal in a first phase over a first downlinkcommunications medium, and transmit the first downlink MIMOcommunications signal wirelessly as a first electrical downlink MIMOcommunications signal over the first MIMO transmitter antenna in thefirst polarization. The first MIMO transmitter is also configured toreceive a second downlink MIMO communications signal in the first phaseover a second downlink communications medium, and transmit the seconddownlink MIMO communications signal wirelessly as a second electricaldownlink MIMO communications signal over the second MIMO transmitterantenna in the second polarization. The second MIMO transmitter isconfigured to receive a third downlink MIMO communications signal in thefirst phase over a third downlink communications medium, and transmitthe third downlink MIMO communications signal wirelessly as a thirdelectrical downlink MIMO communications signal over the third MIMOtransmitter antenna in the first polarization. The second MIMOtransmitter is also configured to receive a fourth downlink MIMOcommunications signal over a fourth downlink communications medium, andtransmit the fourth downlink MIMO communications signal in a secondphase shifted from the first phase, wirelessly as a fourth electricaldownlink MIMO communications signal over the fourth MIMO transmitterantenna in the second polarization.

In another embodiment, a method of transmitting MIMO communicationssignals to wireless client devices in a distributed antenna system isprovided. The method includes receiving a first downlink MIMOcommunications signal in a first phase over a first downlinkcommunications medium. The method also includes transmitting the firstdownlink MIMO communications signal wirelessly as a first electricaldownlink MIMO communications signal over a first MIMO transmitterantenna in a first polarization. The method also includes receiving asecond downlink MIMO communications signal in the first phase over asecond downlink communications medium. The method also includestransmitting the second downlink MIMO communications signal wirelesslyas a second electrical downlink MIMO communications signal over a secondMIMO transmitter antenna in a second polarization. The method alsoincludes receiving a third downlink MIMO communications signal in thefirst phase over a third downlink communications medium. The method alsoincludes transmitting the third downlink MIMO communications signalwirelessly as a third electrical downlink MIMO communications signalover the third MIMO transmitter antenna in the first polarization. Themethod also includes receiving a fourth downlink MIMO communicationssignal over a fourth downlink communications medium. The method alsoincludes transmitting the fourth downlink MIMO communications signal ina second phase shifted from the first phase, wirelessly as a fourthelectrical downlink MIMO communications signal over the fourth MIMOtransmitter antenna in the second polarization.

In another embodiment, a distributed antenna system for distributingMIMO communications signals to wireless client devices is provided. Thedistributed antenna system comprises a central unit. The central unitcomprises a central unit transmitter configured to receive a downlinkcommunications signal. The central unit transmitter is also configuredto transmit the received downlink communications signal as a first MIMOdownlink communications signal over a first downlink communicationsmedium, a second MIMO downlink communications signal over a seconddownlink communications medium, a third MIMO downlink communicationssignal over a third downlink communications medium, and a fourth MIMOdownlink communications signal over a fourth downlink communicationsmedium.

This distributed antenna system also comprises a remote unit. The remoteunit comprises a first MIMO transmitter comprising a first MIMOtransmitter antenna configured to transmit MIMO communications signalsin a first polarization and a second MIMO transmitter antenna configuredto transmit MIMO communications signals in a second polarizationdifferent from the first polarization. The remote unit also comprises asecond MIMO transmitter comprising a third MIMO transmitter antennaconfigured to transmit MIMO communications signals in the firstpolarization and a fourth MIMO transmitter antenna configured totransmit MIMO communications signals in the second polarization. Thefirst MIMO transmitter is configured to receive a first downlink MIMOcommunications signal in a first phase over a first downlinkcommunications medium, and transmit the first downlink MIMOcommunications signal wirelessly as a first electrical downlink MIMOcommunications signal over the first MIMO transmitter antenna in thefirst polarization. The first MIMO transmitter is also configured toreceive a second downlink MIMO communications signal in the first phaseover a second downlink communications medium, and transmit the seconddownlink MIMO communications signal wirelessly as a second electricaldownlink MIMO communications signal over the second MIMO transmitterantenna in the second polarization. The second MIMO transmitter isconfigured to receive a third downlink MIMO communications signal in thefirst phase over a third downlink communications medium, and transmitthe third downlink MIMO communications signal wirelessly as a thirdelectrical downlink MIMO communications signal over the third MIMOtransmitter antenna in the first polarization. The second MIMOtransmitter is also configured to receive a fourth downlink MIMOcommunications signal over a fourth downlink communications medium, andtransmit the fourth downlink MIMO communications signal in a secondphase shifted from the first phase, wirelessly as a fourth electricaldownlink MIMO communications signal over the fourth MIMO transmitterantenna in the second polarization. The remote unit also comprises atleast one phase shifter configured to phase shift the fourth downlinkMIMO communications signal to the second phase.

The distributed antenna systems disclosed herein can be configured tosupport one or more radio-frequency (RF)-based services and/ordistribution of one or more digital data services. The remote units inthe distributed antenna systems may be configured to transmit andreceive wireless communication signal at one or more frequencies,including but not limited to extremely high frequencies (EHF) (i.e.,approximately 30 GHz-approximately 300 GHz). The distributed antennasystems may include, without limitation, wireless local area networks(WLANs). Further, as a non-limiting example, the distributed antennasystems may be an optical fiber-based distributed antenna system, butsuch is not required. An optical fiber-based distributed antenna systemmay employ Radio-over-Fiber (RoF) communications. The embodimentsdisclosed herein are also applicable to other remote antenna clustersand distributed antenna systems, including those that include otherforms of communications media for distribution of communicationssignals, including electrical conductors and wireless transmission. Forexample, the distributed antenna systems may include electrical and/orwireless communications mediums between a central unit and remote unitsin addition or in lieu of optical fiber communications medium. Theembodiments disclosed herein may also be applicable to remote antennaclusters and distributed antenna systems and may also include more thanone communications media for distribution of communications signals(e.g., digital data services, RF communications services). Thecommunications signals in the distributed antenna system may or may notbe frequency shifted.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments, and are intendedto provide an overview or framework for understanding the nature andcharacter of the disclosure. The drawings illustrate variousembodiments, and together with the description serve to explain theprinciples and operation of the concepts disclosed.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic of an exemplary distributed antenna system;

FIG. 2 is a schematic diagram of an exemplary multiple-in, multiple-out(MIMO) optical fiber-based distributed antenna system;

FIG. 3A is a top view diagram of a room having an exemplary MIMO antennasystem comprising two (2) MIMO transmitter antennas in line-of-sight(LOS) with two (2) MIMO receiver antennas to illustrate interference inMIMO communication signals received in the same frequency channel by theMIMO receiver antennas that can cause a MIMO algorithm to fail to solvethe channel matrix;

FIG. 3B is a graph illustrating exemplary measured performancedegradation for a given placement distance between the MIMO transmitterantennas in the MIMO antenna system in FIG. 3A;

FIG. 3C is a graph illustrating an exemplary effective antenna coveragearea in proximity to the MIMO transmitter antennas in FIG. 3A;

FIG. 4A is a schematic diagram of an exemplary MIMO optical fiber-baseddistributed antenna system employing a central unit employing a MIMOtransmitter configured to electrically phase shift at least onetransmitted MIMO electrical downlink communications signal received andtransmitted by a remote unit employing multiple MIMO transmitters eachconfigured with multiple MIMO transmitter antennas configured totransmit in different polarization states;

FIG. 4B is a schematic diagram of an exemplary MIMO optical fiber-baseddistributed antenna system employing an optical phase shifter in anoptical downlink communications medium configured to optically phaseshift at least one transmitted MIMO electrical downlink communicationssignal received and transmitted by a remote unit employing multiple MIMOtransmitters each configured with multiple MIMO transmitter antennasconfigured to transmit in different polarization states;

FIG. 4C is a schematic diagram of an exemplary MIMO optical fiber-baseddistributed antenna system employing remote units employing multipleMIMO transmitters each employing multiple MIMO transmitter antennasconfigured to transmit in different polarization states, wherein one ofthe MIMO electrical downlink communications signals transmitted by oneof the MIMO transmitters in a polarization state is electrically phaseshifted;

FIG. 5A is a graph illustrating exemplary measured performancedegradation for a given placement distance between MIMO transmitterantennas in a MIMO transmitter in a remote unit in the distributedantenna systems in FIGS. 4A-4C, when employing and not employing phaseshifting of at least one transmitted downlink communications signals;

FIG. 5B is a graph illustrating an exemplary effective antenna coveragearea in proximity to the MIMO transmitter antennas of a remote unit inthe distributed antenna systems in FIGS. 4A-4C;

FIG. 5C is a graph illustrating an exemplary effective antenna coverageversus placement distance between MIMO transmitter antennas in a MIMOtransmitter in a remote unit in the distributed antenna systems in FIGS.4A-4C, for a given first placement distance between MIMO receiverantennas, when employing and not employing phase shifting of at leastone transmitted downlink communications signals;

FIG. 5D is a graph illustrating an exemplary effective antenna coverageversus placement distance between MIMO transmitter antennas in a MIMOtransmitter in a remote unit in the distributed antenna systems in FIGS.4A-4C, for a given second placement distance between MIMO receiverantennas, when employing and not employing phase shifting of at leastone transmitted downlink communications signal;

FIG. 6 is a schematic diagram of an exemplary remote unit in a MIMOdistributed antenna system, wherein the remote unit employs multipleMIMO transmitters, and wherein at least one of the MIMO transmittersprovides an offset between its multiple MIMO transmitters antennasconfigured to transmit in different polarization states;

FIG. 7A is a graph illustrating an exemplary effective antenna coverageversus placement distance between MIMO transmitter antennas in a MIMOtransmitter of the remote unit in FIG. 6, for a given first placementdistance between MIMO receiver antennas, when employing and notemploying placement offset between the MIMO transmitter antennas;

FIG. 7B is a graph illustrating an exemplary effective antenna coverageversus placement distance between MIMO transmitter antennas in a MIMOtransmitter of the remote unit in FIG. 6, for a given second placementdistance between MIMO receiver antennas, when employing and notemploying placement offset between MIMO transmitter antennas;

FIG. 7C is a graph illustrating an exemplary effective antenna coveragefor a given placement distance between MIMO transmitter antennas, in aMIMO transmitter of the remote unit in FIG. 6, for a given placementdistance between MIMO receiver antennas, when employing and notemploying placement offset between MIMO transmitter antennas; and

FIG. 8 is a schematic diagram of a generalized representation of anexemplary controller that can be included in any central unit, remoteunits, wireless client devices, and/or any other components ofdistributed antenna systems to reduce or eliminate issues with a MIMOalgorithm solving the channel matrix for transmitted MIMO electricaldownlink communications signals.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments, examples ofwhich are illustrated in the accompanying drawings, in which some, butnot all embodiments are shown. Indeed, the concepts may be embodied inmany different forms and should not be construed as limiting herein;rather these embodiments are provided so that this disclosure willsatisfy applicable legal requirements. Whenever possible, like referencenumbers will be used to refer to like components or parts.

Components, systems, and methods for reducing location-basedinterference in distributed antenna systems operating in multiple-input,multiple-output (MIMO) configuration are disclosed. The distributedantenna systems include remote units employing MIMO transmittersconfigured to transmit multiple data streams in MIMO configuration toMIMO receivers in wireless client devices. Interference is defined asissues with received MIMO communications signals that can cause a MIMOalgorithm to not be able to solve a channel matrix for MIMOcommunications signals received by MIMO receivers in client devices.These issues can occur due to lack of spatial (i.e., phase) separationin the received MIMO communications signals, especially with closelylocated MIMO transmitters configured for line-of-sight (LOS)communications. Thus, to provide phase separation of MIMO communicationsignals received by MIMO receivers in client devices, multiple MIMOtransmitters in a remote unit are each configured to employ multipletransmitter antennas, that are each configured to transmit in differentpolarization states. In certain embodiments, one of the MIMOcommunications signals is phase shifted in one of the polarizationstates to provide phase separation between MIMO communication signalsreceived by the MIMO receivers. In other embodiments, multipletransmitter antennas in a MIMO transmitter can be offset to providephase separation.

Before discussing examples of components, systems, and methods forreducing location-based interference in distributed antenna systemsoperating in MIMO configuration starting at FIG. 4A, an exemplarydistributed antenna system is described in regard to FIGS. 1-3C. In thisregard, FIG. 1 is a schematic diagram of a conventional distributedantenna system 10. The distributed antenna system 10 is an opticalfiber-based distributed antenna system. The distributed antenna system10 is configured to create one or more antenna coverage areas forestablishing communications with wireless client devices located in theradio frequency (RF) range of the antenna coverage areas. In anexemplary embodiment, the distributed antenna system 10 may provide RFcommunication services (e.g., cellular services). As illustrated, thedistributed antenna system 10 includes a central unit 12, one or moreremote units 14, and an optical fiber 16 that optically couples thecentral unit 12 to the remote unit 14. The central unit 12 may also bereferred to as a head-end unit. The remote unit 14 is a type of remotecommunications unit, and may also be referred to as a “remote antennaunit.” In general, a remote communications unit can support wirelesscommunications or wired communications, or both. The central unit 12 isconfigured to receive communications over downlink electrical RF signals18D from a source or sources, such as a network or carrier as examples,and provide such communications to the remote unit 14. The central unit12 is also configured to return communications received from the remoteunit 14, via uplink electrical RF signals 18U, back to the source orsources. In this regard, in this embodiment, the optical fiber 16includes at least one downlink optical fiber 16D to carry signalscommunicated from the central unit 12 to the remote unit 14 and at leastone uplink optical fiber 16U to carry signals communicated from theremote unit 14 back to the central unit 12.

One downlink optical fiber 16D and one uplink optical fiber 16U could beprovided to support multiple full-duplex channels each usingwave-division multiplexing (WDM), as discussed in U.S. patentapplication Ser. No. 12/892,424, entitled “Providing Digital DataServices in Optical Fiber-based Distributed Radio Frequency (RF)Communications Systems, And Related Components and Methods,”incorporated herein by reference in its entirety. Other options for WDMand frequency-division multiplexing (FDM) are also disclosed in U.S.patent application Ser. No. 12/892,424, any of which can be employed inany of the embodiments disclosed herein. Further, U.S. patentapplication Ser. No. 12/892,424 also discloses distributed digital datacommunications signals in a distributed antenna system which may also bedistributed in the distributed antenna system 10 either in conjunctionwith the RF communications signals or not.

The distributed antenna system 10 has an antenna coverage area 20 thatcan be disposed about the remote unit 14. The antenna coverage area 20of the remote unit 14 forms an RF coverage area 21. The central unit 12is adapted to perform or to facilitate any one of a number ofRadio-over-Fiber (RoF) applications, such as RF identification (RFID),wireless local-area network (WLAN) communication, or cellular phoneservice. Shown within the antenna coverage area 20 is a client device 24in the form of a mobile device, which may be a cellular telephone as anexample. The client device 24 can be any device that is capable ofreceiving RF communications signals. The client device 24 includes anantenna 26 (e.g., a wireless card) adapted to receive and/or sendelectromagnetic RF signals.

With continuing reference to FIG. 1, to communicate the electrical RFsignals over the downlink optical fiber 16D to the remote unit 14, to inturn be communicated to the client device 24 in the antenna coveragearea 20 formed by the remote unit 14, the central unit 12 includes aradio interface in the form of an electrical-to-optical (E/O) converter28. The E/O converter 28 converts the downlink electrical RF signals 18Dto downlink optical RF signals 22D to be communicated over the downlinkoptical fiber 16D. The remote unit 14 includes an optical-to-electrical(O/E) converter 30 to convert the received downlink optical RF signals22D back to electrical RF signals to be communicated wirelessly throughan antenna 32 of the remote unit 14 to the client device 24 located inthe antenna coverage area 20.

Similarly, the antenna 32 is also configured to receive wireless RFcommunications from the client device 24 in the antenna coverage area20. In this regard, the antenna 32 receives wireless RF communicationsfrom the client device 24 and communicates electrical RF signalsrepresenting the wireless RF communications to an E/O converter 34 inthe remote unit 14. The E/O converter 34 converts the electrical RFsignals into uplink optical RF signals 22U to be communicated over theuplink optical fiber 16U. An O/E converter 36 provided in the centralunit 12 converts the uplink optical RF signals 22U into uplinkelectrical RF signals, which can then be communicated as uplinkelectrical RF signals 18U back to a network or other source.

As noted, one or more of the network or other sources can be a cellularsystem, which may include a base station or base transceiver station(BTS). The BTS may be provided by a second party such as a cellularservice provider, and can be co-located or located remotely from thecentral unit 12.

In a typical cellular system, for example, a plurality of BTSs isdeployed at a plurality of remote locations to provide wirelesstelephone coverage. Each BTS serves a corresponding cell and when amobile client device enters the cell, the BTS communicates with themobile client device. Each BTS can include at least one radiotransceiver for enabling communication with one or more subscriber unitsoperating within the associated cell. As another example, wirelessrepeaters or bi-directional amplifiers could also be used to serve acorresponding cell in lieu of a BTS. Alternatively, radio input could beprovided by a repeater, picocell, or femtocell, as other examples. In aparticular exemplary embodiment, cellular signal distribution in thefrequency range from 400 MHz to 2.7 GHz is supported by the distributedantenna system 10.

Although the distributed antenna system 10 in FIG. 1 allows fordistribution of radio frequency (RF) communications signals; thedistributed antenna system 10 is not limited to distribution of RFcommunications signals. Data communications signals, including digitaldata signals, for distributing data services could also be distributedin the distributed antenna system 10 in lieu of or in addition to RFcommunications signals. Also note that while the distributed antennasystem 10 in FIG. 1 discussed below includes distribution ofcommunications signals over optical fiber, the distributed antennasystem 10 is not limited to distribution of communications signals overoptical fiber. Distribution media could also include, but are notlimited to, coaxial cable, twisted-pair conductors, wirelesstransmission and reception, and any combination thereof. Also, anycombination can be employed that also involves optical fiber forportions of the distributed system.

A distributed antenna system, including the distributed antenna system10 in FIG. 1, can be configured in MIMO configuration for MIMOoperation. In this regard, FIG. 2 illustrates a schematic diagram of anexemplary MIMO optical fiber-based distributed antenna system 40(hereinafter referred to as “MIMO distributed antenna system 40”). TheMIMO distributed antenna system 40 is configured to operate in MIMOconfiguration. MIMO technology involves the use of multiple antennas atboth a transmitter and receiver to improve communication performance. Inthis regard, a central unit 42 is provided that is configured todistribute downlink communications signals to one or more remote units44. FIG. 2 only illustrates one remote unit 44, but note that aplurality of remote units 44 is typically provided. The remote units 44are configured to wirelessly communicate the downlink communicationsignals to one or more client devices 46 that are in communication rangeof the remote unit 44. The remote units 44 may also be referred to as“remote antenna units 44” because of their wireless transmission overantenna functionality. The remote unit 44 is also configured to receiveuplink communication signals from the client devices 46 to bedistributed to the central unit 42. In this embodiment, an optical fibercommunications medium 47 comprising at least one downlink optical fiber48D and at least one uplink optical fiber 48U is provided tocommutatively couple the central unit 42 to the remote units 44. Thecentral unit 42 is also configured to receive uplink communicationsignals from the remote units 44 via the optical fiber communicationsmedium 47, although more specifically over the at least one uplinkoptical fiber 48U. The client device 46 in communication with the remoteunit 44 can provide uplink communication signals to the remote unit 44which are then distributed over the optical fiber communications medium47 to the remote unit 44 to be provided to a network or other source,such as a base station for example.

With continuing reference to FIG. 2, more detail will be discussedregarding the components of the central unit 42, the remote unit 44, andthe client device 46 and the distribution of downlink communicationssignals. The central unit 42 is configured to receive electricaldownlink MIMO communication signals 50D from outside the MIMOdistributed antenna system 40 in a signal processor 52 and provideelectrical uplink communications signals 50U received from clientdevices 46, to other systems. The signal processor 52 is configured toprovide the electrical downlink communication signals 50D to a mixer 60,which may be an IQ signal mixer in this example. The mixer 60 in thisembodiment is configured to convert the electrical downlink MIMOcommunication signals 50D to IQ signals. The mixer 60 is driven by afrequency signal 56 that is provided by a local oscillator 58. Frequencyconversion is optional. In this embodiment, it is desired to up-convertthe frequency of the electrical downlink MIMO communication signals 50Dto a higher frequency to provide electrical downlink MIMO communicationsignals 66D to provide for a greater bandwidth capability beforedistributing the electrical downlink MIMO communications signals 66D tothe remote units 44. For example, the up-conversion carrier frequencymay be provided as an extremely high frequency (e.g. approximately 30GHz to 300 GHz).

With continuing reference to FIG. 2, because the communication mediumbetween the central unit 42 and the remote unit 44 is the optical fibercommunications medium 47, the electrical downlink MIMO communicationsignals 66D are converted to optical signals by an electro-opticalconverter 67. The electro-optical converter 67 includes components toreceive a light wave 68 from a light source 70, such as a laser. Thelight wave 68 is modulated by the frequency oscillations in theelectrical downlink MIMO communication signals 66D to provide opticaldownlink MIMO communication signals 72D to be communicated over thedownlink optical fiber 48D to the remote unit 44. The electro-opticalconverter 67 may be provided so that the electrical downlink MIMOcommunication signals 66D are provided as radio-over-fiber (RoF)communications signals over the downlink optical fiber 48D.

With continuing reference to FIG. 2, the optical downlink MIMOcommunication signals 72D are received by an optical bi-directionalamplifier 74, which is then provided to a MIMO splitter 76 in the remoteunit 44. The MIMO splitter 76 is provided so that the optical downlinkMIMO communication signals 72D can be split among two separatecommunication paths 77(1), 77(2) to be radiated over two separate MIMOtransmitter antennas 78(1), 78(2) provided in two separate MIMOtransmitters 79(1), 79(2) configured in MIMO configuration. The MIMOsplitter 76 in the remote unit 44 is an optical splitter since thereceived optical downlink MIMO communication signals 72D are opticalsignals. In each communication path 77(1), 77(2), optical-to-electricalconverters 80(1), 80(2) are provided to convert the optical downlinkMIMO communication signals 72D to electrical downlink MIMO communicationsignals 82D(1), 82D(2). In this embodiment, as will be discussed in moredetail below, a delay element 84 is provided in one of the transmissionpaths 77(1), 77(2) to phase shift one of the optical downlink MIMOcommunication signals 72D(1), 72D(2) transmitted over one of the MIMOtransmitter antennas 78(1), 78(2) to reduce or eliminate issues with aMIMO algorithm solving the channel matrix for received electricaldownlink MIMO communication signals 82D by the client device 46.

With continuing reference to FIG. 2, the client device 46 includes twoMIMO receivers 85(1), 85(2) that include MIMO receiver antennas 86(1),86(2) also configured in MIMO configuration. The MIMO receiver antennas86(1), 86(2) are configured to receive the electrical downlink MIMOcommunication signals 82D(1), 82D(2) wirelessly from the remote unit 44.Mixers 88(1), 88(2) are provided and coupled to the MIMO receiverantennas 86(1), 86(2) in the client device 46 to provide frequencyconversion of the electrical downlink MIMO communication signals 82D(1),82D(2). In this regard, a local oscillator 90 is provided that isconfigured to provide oscillation signals 92(1), 92(2) to the mixers88(1), 88(2), respectively, for frequency conversion. In thisembodiment, the electrical downlink MIMO communications signals 82D(1),82D(2) are down converted back to their native frequency as received bythe central unit 42. The down converted electrical downlink MIMOcommunication signals 82D(1), 82D(2) are then provided to a signalanalyzer 92 in the client device 46 for any processing desired.

FIG. 3A illustrates a top view of a room 100 employing the exemplaryMIMO distributed antenna system 40 in FIG. 2 to discuss performance ofMIMO communications as affected by antenna placement. As illustrated inFIG. 3A, the two MIMO transmitter antennas 78(1), 78(2) of the remoteunit 44 are shown as being located in the room 100. Similarly, a clientdevice 46 is shown with its two MIMO receiver antennas 86(1), 86(2)configured to receive the electrical downlink MIMO communication signals82D(1), 82D(2) from the two MIMO transmitter 81(1), 81(2) (FIG. 2) inMIMO configuration. The MIMO transmitter antennas 78(1), 78(2) in theMIMO transmitter 81(1), 81(2) in the remote unit 44 are separated by adistance D₁. The MIMO receiver antennas 86(1), 86(2) in the clientdevice 46 are separated by a distance D₂. Issues can arise with MIMOalgorithm being able to solve the channel matrix for received electricaldownlink MIMO communication signals 82D(1), 82D(2) at the client device46 as a function of the distance between the MIMO transmitter antennas78(1), 78(2) in the remote unit 44, the distance between MIMO receiverantennas 86(1), 86(2) in the client device 46, and the distance D₃between remote unit 44 and the client device 46. These issues are alsoreferred to herein as interference issues.

A MIMO algorithm not being able to solve a channel matrix for thereceived electrical downlink MIMO communication signals 82D(1), 82D(2)can negatively affect communications performance. These issues withelectrical downlink MIMO communication signals 82D(1), 82D(2) receivedby the MIMO receiver antennas 86(1), 86(2) can occur due to lack ofspatial (i.e., phase) separation in the received electrical downlinkMIMO communication signals 82D(1), 82D(2), especially in line-of-sight(LOS) communications. To illustrate the effect of these issues, FIG. 3Billustrates a graph 102 illustrating the exemplary measured performancedegradation for a given placement distance between the MIMO transmitterantennas 78(1), 78(2) in FIG. 3A. The graph 102 in FIG. 3B illustratesthe capacity on the y-axis in Gigabits per second (Gbs/s) versus theMIMO transmitter antennas 78(1), 78(2) separation distance D₁ incentimeters. As illustrated in the graph 102, at separation distances D₁of approximately 42 centimeters (cm) and 85 cm, the communicationscapacity illustrated by a capacity curve 104 is severely degraded forthe received electrical downlink MIMO communication signals 82D(1),82D(2) by the MIMO receiver antennas 86(1), 86(2). Even at otherdistances, the capacity is severely degraded, as illustrated in thecapacity curve 104. A degradation curve 106 in FIG. 3B illustrates theeffect of a MIMO algorithm not being able to solve a channel matrix,which is complementary to the capacity curve 104.

FIG. 3C illustrates a graph 108 representing an exemplary effectivecommunication coverage area provided by the distributed antenna system40 in FIG. 2 according to the MIMO transmitter antennas 78(1), 78(2),separation distance D₁, the MIMO receiver antennas 86(1), 86(2),separation distance D₂ in FIG. 3A, and distance therebetween D₃. Asillustrated in FIG. 3C, a desired antenna coverage area 109 is shown asbeing provided by the area formed inside a boundary line 110. However,an actual communication coverage area 113 for the remote unit 44 isprovided inside the boundary line 112, illustrating the effect inreduction communication range of the remote unit 44.

To address these issues, FIGS. 4A-7C are provided to illustrateexemplary distributed antenna systems configured to reducelocation-based interference in distributed antenna systems operating inmultiple-input, multiple-output (MIMO) configuration. In theseembodiments, to provide phase separation of MIMO communication signalsreceived by MIMO receivers in client devices, multiple MIMO transmittersin a remote unit are each configured to employ multiple transmitterantennas. The multiple transmitter antennas are each configured totransmit communications signals in different polarization states. Incertain embodiments, one of the MIMO communications signals is phaseshifted in one of the polarization states to provide phase separationbetween MIMO communication signals received by the MIMO receivers.

In this regard, FIG. 4A illustrates an alternative MIMO distributedantenna system 40(1) similar to the MIMO distributed antenna system 40in FIG. 2. The MIMO distributed antenna system 40(1) in FIG. 4A isconfigured to reduce or eliminate the inability of a MIMO algorithm notbeing able to solve a channel matrix of received downlink communicationsignals at a MIMO receiver in a client device based on the separationdistance between MIMO transmitter antennas in a MIMO transmitter of aremote unit to reduce or eliminate performance degradation such as shownin FIGS. 3B and 3C above. The MIMO distributed antenna system 40(1) mayinclude the same components in the MIMO distributed antenna system 40 inFIG. 2 unless otherwise noted in FIG. 4A.

With continuing reference to FIG. 4A, a central unit 42(1) is configuredto receive the electrical downlink MIMO communications signals 50D asdiscussed in regard to FIG. 2. However, a signal processor 52(1) isconfigured to split the electrical downlink MIMO communications signals50D into four (4) electrical downlink MIMO communications signals50D(1)-50D(4) over four separate channels. A delay element 122 isprovided in the central unit 42(1) to phase shift at least one of theelectrical downlink MIMO communications signals 50D. Note that althoughthe electrical downlink MIMO communications signal 50D(4) in thisexample, any other(s) downlink MIMO communications signal(s)50D(1)-50D(3) could be phase shifted. The delay element 122 may be atunable delay element that can be programmed or controlled to controlthe amount of phase shift, if desired. As will be discussed in moredetail below, the phase shifting of one of the electrical downlink MIMOcommunications signals 50D will allow one of the polarization statesprovided by one of MIMO transmitters in a remote unit 44(1) to includephase separation between first through fourth electrical downlink MIMOcommunication signals 82D(1)-82D(4) that are received by the MIMOreceivers to reduce or eliminate the inability of a MIMO algorithm tosolve a channel matrix. Turning back to the central unit 42(1),electro-optical converters 67(1)-67(4) are provided to convert theelectrical downlink MIMO communications signals 50D(1)-50D(4) intooptical downlink MIMO communications signals 72D(1)-72D(4) provided overoptical fiber communications medium 47(1).

With continuing reference to FIG. 4A, the remote unit 44(1) includes twoMIMO transmitters 124(1), 124(2) in MIMO configuration. However, theMIMO transmitters 124(1), 124(2) each include two MIMO transmitterantennas 126(1)(1), 126(1)(2), and 126(2)(1), 126(2)(2). The first MIMOtransmitter 124(1) includes the first MIMO transmitter antenna 126(1)(1)configured to radiate the first electrical downlink MIMO communicationssignals 82D(1) (after conversion from optical to electrical signals) ina first polarization 128(1), as indicated in FIG. 4A. The first MIMOtransmitter 124(1) also includes the second MIMO transmitter antenna126(1)(2) configured to radiate the second electrical downlink MIMOcommunications signal 82D(2) in a second polarization 128(2) differentfrom the first polarization 128(1). In this manner, the first and secondelectrical downlink MIMO communications signals 82D(1), 82D(2) can bereceived by two different MIMO receiver antennas 130(1), 130(2) in MIMOreceivers 132(1), 132(2), respectively, each configured to receivesignals in different polarizations 128(1), 128(2) among the first andsecond polarizations 128(1), 128(2) without the MIMO algorithm beingunable to solve the channel matrix. Thus, the MIMO receivers 132(1),132(2) can receive the first and second electrical downlink MIMOcommunications signal 82D(1), 82D(2) in different polarizations 128(1),128(2), respectively, from the first MIMO transmitter 124(1) so that aMIMO algorithm can solve the channel matrix for the first and secondelectrical downlink MIMO communications signal 82D(1), 82D(2). In thisembodiment, the first polarization 128(1) is configured to be orthogonalto the second polarization 128(2) to maximize avoidance of the MIMOreceivers 132(1), 132(2) receiving the incorrect electrical downlinkMIMO communications signal 82D(1), 82D(2), but this configuration is notrequired.

With continuing reference to FIG. 4A, the second MIMO transmitter 124(2)in the remote unit 44(1) includes a third MIMO transmitter antenna126(2)(1) configured to radiate the third electrical downlink MIMOcommunications signals 82D(3) (after conversion from optical toelectrical signals) in the first polarization 128(1), as indicated inFIG. 4A. The second MIMO transmitter 124(2) also includes the fourthMIMO transmitter antenna 126(2)(2) configured to radiate the fourthelectrical downlink MIMO communications signal 82D(4) in the secondpolarization 128(2) different from the first polarization 128(1). Inthis manner, the third and fourth electrical downlink MIMOcommunications signals 82D(3), 82D(4) can also be received by the twodifferent MIMO receiver antennas 130(1), 130(2) in MIMO receivers132(1), 132(2), respectively, each configured to receive signals indifferent polarizations 128(1), 128(2) among the first and secondpolarizations 128(1), 128(2). Thus, the MIMO receivers 132(1), 132(2)can receive the third and fourth electrical downlink MIMO communicationssignal 82D(3), 82D(4) in different polarizations, respectively, from thesecond MIMO transmitter 124(2) between the third and fourth electricaldownlink MIMO communications signal 82D(3), 82D(4). The electricaldownlink MIMO communications signals 82D(1)-82D(4) are received by theMIMO receivers 132(1), 132(2) and provided to a signal processor 134 anda MIMO processor 136 for processing.

As previously discussed above, the delay element 122 is provided in thecentral unit 42(1) to phase shift the electrical downlink MIMOcommunications signal 50D(4). This phase shift in turn causes the secondand fourth electrical downlink MIMO communications signals 82D(2),82D(4) to be received by the second MIMO receiver antennas 130(2) out ofphase with the receipt of the first and third electrical downlink MIMOcommunications signals 82D(1), 82D(3) by the first MIMO receiver 132(1)which are in the first polarization 128(1). This reduces or eliminatethe first and third electrical downlink MIMO communications signals82D(1), 82D(3) being received by the first MIMO receiver 132(1) and thesecond and fourth electrical downlink MIMO communications signals82D(2), 82D(4) being received by the second MIMO receiver 132(2).

The phase shift can be provided in other areas of a MIMO distributedantenna system other than in the central unit, as provided in the MIMOdistributed antenna system 40(1) in FIG. 4A. In this regard, FIG. 4B isa schematic diagram of another MIMO optical fiber-based distributedantenna system 40(2) (“MIMO distributed antenna system 40(2)”) employinga delay element 140 in the form of an optical phase shifter in theoptical fiber communications medium 47(1). The delay element 140 can betunable to allow for the phase shift to be controlled and tuned. Thedelay element 140 may be an additional length of optical fiber to makethe corresponding downlink optical fibers in the optical fibercommunications medium 47(1) carrying the optical downlink MIMOcommunications signal 72D(1) longer than the other downlink opticalfibers of the optical fiber communications medium 47(1). Common elementsbetween the MIMO distributed antenna system 40(1) in FIG. 4A and theMIMO distributed antenna system 40(2) in FIG. 4B are noted with commonelement numbers and will not be re-described. In this embodiment, thedelay element 140 is configured to optically phase shift the opticaldownlink MIMO communications signal 72D(4) received by the second MIMOtransmitter 124(2) and transmitted by the second MIMO transmitter 124(2)to the client device 46(1). The central unit 42(2) in FIG. 4B does notinclude a delay element to phase shift downlink electricalcommunications signals like provided in the central unit 42(1) in FIG.4A.

As previously discussed above with regard to FIGS. 4A and 4B, a delayelement can be provided in the central unit 42(1), 42(2) and/or theoptical fiber communications medium 47(1) to phase shift the electricaldownlink MIMO communications signal 50D(4). In this regard, FIG. 4C is aschematic diagram of another MIMO optical fiber-based distributedantenna system 40(3) (“MIMO distributed antenna system 40(3)”) employinga delay element 142 in the form of an electrical phase shifter in theremote unit 44(2). Common elements between the MIMO distributed antennasystem 40(3) in FIG. 4C and the MIMO distributed antenna systems 40(1),40(2) in FIGS. 4A and 4B are noted with common element numbers and willnot be re-described. In this embodiment, a signal processor 144 in theremote unit 44(2) receives the optical downlink MIMO communicationssignals 72D(1)-72D(4) and converts these signals into electricaldownlink MIMO communications signals 82D(1)-82D(4) in anoptical-to-electrical converter. The delay element 142 is configured toelectrically phase shift the electrical downlink MIMO communicationssignal 82D(4) received and transmitted by the second MIMO transmitter124(2) in the remote unit 44(2) to the client device 46(1) so that aMIMO algorithm can solve the channel matrix for the electrical downlinkMIMO communications signal 82D(1)-82D(4).

To illustrate the performance in the MIMO distributed antenna systems40(1)-40(3) in FIGS. 4A-4C, FIG. 5A illustrates a graph 150 illustratingthe exemplary measured performance degradation for a given placementdistance between the MIMO transmitters 124(1), 124(2). The graph 102 inFIG. 3B illustrates the capacity on the y-axis in Gigabits per second(Gbs/s) versus the MIMO transmitter antennas 78(1), 78(2) separationdistance in centimeters. As illustrated in the graph 150, for a givenseparation distance the communications capacity illustrated by acapacity curve 152 is not substantially degraded for received electricaldownlink MIMO communication signals 82D(1), 82D(2) by the MIMO receiverantennas 86(1), 86(2). The degradation curve 154 in FIG. 5A illustratesthe effect of a MIMO algorithm having issues solving a channel matrixthat may be present when techniques described above for MIMO distributedantenna systems 40(1)-40(3) are not employed. FIG. 5B illustrates agraph 160 representing an exemplary effective communication coveragearea provided by the MIMO distributed antenna systems 40(1)-40(3) inFIGS. 4A-4C according to the MIMO transmitter 124(1), 124(2) separatedby a given distance. As illustrated in FIG. 5B, a desired antennacoverage area 162 is shown as being provided by the area formed insidethe boundary line 164.

FIG. 5C is a graph 170 illustrating an exemplary effective antennacoverage versus placement distance between MIMO transmitters 124(1),124(2) in the distributed antenna systems 40(1)-40(3) in FIGS. 4A-4C,for a two (2) cm placement distance between the MIMO receivers 132(1),132(2). FIG. 5D is a graph 180 illustrating an exemplary effectiveantenna coverage versus placement distance between MIMO transmitters124(1), 124(2) in the distributed antenna systems 40(1)-40(3) in FIGS.4A-4C, for a 10 cm placement distance between the MIMO receives 132(1),132(2). Coverage curves 172, 182 illustrate the capacity when thetechniques described above for the MIMO distributed antenna systems40(1)-40(3) are employed. Coverage curves 174, 184 illustrate thecapacity that may be present when the techniques described above for theMIMO distributed antenna systems 40(1)-40(3) are not employed.

Other configurations and techniques may also be possible to providephase separation of MIMO communication signals received by MIMOreceivers in client devices, multiple MIMO transmitters in a remote unitare each configured to employ multiple transmitter antennas. In thisregard, FIG. 6 is a schematic diagram of another exemplary remote unit44(3) that provides phase separation of the downlink electrical MIMOcommunication signals 82D(1)-82D(4) received by the MIMO receivers132(1), 132(2). The remote unit 44(3) may be employed in a MIMOdistributed antenna system, including the MIMO distributed antennasystems 40(1)-140(3) described in FIGS. 4A-4C above. Common elementsbetween the components in FIG. 6 and the MIMO distributed antennasystems 40(1)-40(3) in FIGS. 4A-4C are noted with common element numbersand will not be re-described. In this embodiment, instead of providing adelay element to provide phase shift, the MIMO transmitter antennas126(1)(1), 126(1)(2) in the MIMO transmitter 124(1), 124(2) are offsetin distance at distance D₄. A small offset distance may be sufficient tosignificantly improve capacity. This separation distance provides aphase shift in the electrical downlink MIMO communications signal82D(1).

FIG. 7A is a graph 190 illustrating an exemplary effective antennacoverage versus placement distance between MIMO transmitters 124(1),124(2) in a MIMO distributed antenna system 40(1)-40(3) employing theremote unit 44(3) in FIG. 6, for a two (2) cm placement distance betweenthe MIMO receivers 132(1), 132(2). FIG. 7B is a graph 200 illustratingan exemplary effective antenna coverage versus placement distancebetween MIMO transmitters 124(1), 124(2) in a MIMO distributed antennasystem 40(1)-40(3) employing the remote unit 44(3) in FIG. 6, for a ten(10) cm placement distance between the MIMO receivers 132(1), 132(2).Coverage curves 192, 202 illustrate the capacity when the remote unit44(3) is employed. Coverage curves 194, 204 illustrate the capacity thatmay be present when the techniques described above for the MIMOdistributed antenna systems 40(1)-40(3) and the remote unit 44(3) arenot employed. FIG. 7C is a graph 210 illustrating an exemplary effectiveantenna coverage for a given offset distance between MIMO transmitterantennas 126(1)(1), 126(1)(2) in the first MIMO transmitter 124(1) ofthe remote unit 44(3) in FIG. 6.

It may also be desired to provide high-speed wireless digital dataservice connectivity with remote units in the MIMO distributed antennasystems disclosed herein. One example would be WiFi. WiFi was initiallylimited in data rate transfer to 12.24 Mb/s and is now provided at datatransfer rates of up to 54 Mb/s using WLAN frequencies of 2.4 GHz and5.8 GHz. While interesting for many applications, WiFi has proven tohave too small a bandwidth to support real time downloading ofuncompressed high definition (HD) television signals to wireless clientdevices. To increase data transfer rates, the frequency of wirelesssignals could be increased to provide larger channel bandwidth. Forexample, an extremely high frequency in the range of 30 GHz to 300 GHzcould be employed. For example, the sixty (60) GHz spectrum is an EHFthat is an unlicensed spectrum by the Federal Communications Commission(FCC) and that could be employed to provide for larger channelbandwidths. However, high frequency wireless signals are more easilyattenuated or blocked from traveling through walls or other buildingstructures where distributed antenna systems are installed.

Thus, the embodiments disclosed herein can include distribution ofextremely high frequency (EHF) (i.e., approximately 30-approximately 300GHz), as a non-limiting example. The MIMO distributed antenna systemsdisclosed herein can also support provision of digital data services towireless clients. The use of the EHF band allows for the use of channelshaving a higher bandwidth, which in turn allows more data intensivesignals, such as uncompressed HD video to be communicated withoutsubstantial degradation to the quality of the video. As a non-limitingexample, the distributed antenna systems disclosed herein may operate atapproximately sixty (60) GHz with approximately seven (7) GHz bandwidthchannels to provide greater bandwidth to digital data services. Thedistributed antenna systems disclosed herein may be well suited to bedeployed in an indoor building or other facility for delivering ofdigital data services.

It may be desirable to provide MIMO distributed antenna systems,according to the embodiments disclosed herein, that provide digital dataservices for client devices. For example, it may be desirable to providedigital data services to client devices located within a distributedantenna system. Wired and wireless devices may be located in thebuilding infrastructures that are configured to access digital dataservices. Examples of digital data services include, but are not limitedto, Ethernet, WLAN, WiMax, WiFi, DSL, and LTE, etc. Ethernet standardscould be supported, including but not limited to, 100 Mb/s (i.e., fastEthernet) or Gigabit (Gb) Ethernet, or ten Gigabit (10G) Ethernet.Examples of digital data services include, but are not limited to, wiredand wireless servers, wireless access points (WAPs), gateways, desktopcomputers, hubs, switches, remote radio heads (RRHs), baseband units(BBUs), and femtocells. A separate digital data services network can beprovided to provide digital data services to digital data devices.

FIG. 8 is a schematic diagram representation of additional detailillustrating components that could be employed in any of the componentsor devices disclosed herein, but only if adapted to execute instructionsfrom an exemplary computer-readable medium to perform any of thefunctions or processing described herein. In this regard, such componentor device may include a computer system 220 within which a set ofinstructions for performing any one or more of the location servicesdiscussed herein may be executed. The computer system 220 may beconnected (e.g., networked) to other machines in a LAN, an intranet, anextranet, or the Internet. While only a single device is illustrated,the term “device” shall also be taken to include any collection ofdevices that individually or jointly execute a set (or multiple sets) ofinstructions to perform any one or more of the methodologies discussedherein. The computer system 220 may be a circuit or circuits included inan electronic board card, such as, a printed circuit board (PCB), aserver, a personal computer, a desktop computer, a laptop computer, apersonal digital assistant (PDA), a computing pad, a mobile device, orany other device, and may represent, for example, a server or a user'scomputer.

The exemplary computer system 220 in this embodiment includes aprocessing device or processor 222, a main memory 224 (e.g., read-onlymemory (ROM), flash memory, dynamic random access memory (DRAM), such assynchronous DRAM (SDRAM), etc.), and a static memory 226 (e.g., flashmemory, static random access memory (SRAM), etc.), which may communicatewith each other via a data bus 228. Alternatively, the processing device222 may be connected to the main memory 224 and/or static memory 226directly or via some other connectivity means. The processing device 222may be a controller, and the main memory 224 or static memory 226 may beany type of memory.

The processing device 222 represents one or more general-purposeprocessing devices, such as a microprocessor, central processing unit,or the like. More particularly, the processing device 222 may be acomplex instruction set computing (CISC) microprocessor, a reducedinstruction set computing (RISC) microprocessor, a very long instructionword (VLIW) microprocessor, a processor implementing other instructionsets, or other processors implementing a combination of instructionsets. The processing device 222 is configured to execute processinglogic in instructions 230 for performing the operations and stepsdiscussed herein.

The computer system 220 may further include a network interface device232. The computer system 220 also may or may not include an input 234,configured to receive input and selections to be communicated to thecomputer system 220 when executing instructions. The computer system 220also may or may not include an output 236, including but not limited toa display, a video display unit (e.g., a liquid crystal display (LCD) ora cathode ray tube (CRT)), an alphanumeric input device (e.g., akeyboard), and/or a cursor control device (e.g., a mouse).

The computer system 220 may or may not include a data storage devicethat includes instructions 238 stored in a computer-readable medium 240.The instructions 238 may also reside, completely or at least partially,within the main memory 224 and/or within the processing device 222during execution thereof by the computer system 220, the main memory 224and the processing device 222 also constituting computer-readablemedium. The instructions 238 may further be transmitted or received overa network 242 via the network interface device 232.

While the computer-readable medium 240 is shown in an exemplaryembodiment to be a single medium, the term “computer-readable medium”should be taken to include a single medium or multiple media (e.g., acentralized or distributed database, and/or associated caches andservers) that store the one or more sets of instructions. The term“computer-readable medium” shall also be taken to include any mediumthat is capable of storing, encoding, or carrying a set of instructionsfor execution by the processing device and that cause the processingdevice to perform any one or more of the methodologies of theembodiments disclosed herein.

The embodiments disclosed herein include various steps. The steps of theembodiments disclosed herein may be formed by hardware components,software components, and combinations thereof.

The embodiments disclosed herein may be provided as a computer programproduct, or software, that may include a machine-readable medium (orcomputer-readable medium) having stored thereon instructions, which maybe used to program a computer system (or other electronic devices) toperform a process according to the embodiments disclosed herein.

Unless specifically stated otherwise and as apparent from the previousdiscussion, it is appreciated that throughout the description,discussions utilizing terms such as “processing,” “computing,”“determining,” “displaying,” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data and memories represented asphysical (electronic) quantities within the computer system's registersinto other data similarly represented as physical quantities within thecomputer system memories or registers or other such information storage,transmission, or display devices.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. In addition, theembodiments described herein are not described with reference to anyparticular programming language.

Those of skill in the art will further appreciate that the variousillustrative logical blocks, modules, circuits, and algorithms describedin connection with the embodiments disclosed herein may be implementedas electronic hardware, instructions stored in memory or in anothercomputer-readable medium and executed by a processor or other processingdevice, or combinations of both. The components of the distributedantenna systems described herein may be employed in any circuit,hardware component, integrated circuit (IC), or IC chip, as examples.Memory disclosed herein may be any type and size of memory and may beconfigured to store any type of information desired. To clearlyillustrate this interchangeability, various illustrative components,blocks, modules, circuits, and steps have been described above generallyin terms of their functionality. How such functionality is implementeddepends on the particular application, design choices, and/or designconstraints imposed on the overall system.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a processor, a Digital Signal Processor (DSP), anApplication Specific Integrated Circuit (ASIC), a Field ProgrammableGate Array (FPGA), or other programmable logic device, a discrete gateor transistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Furthermore,a controller may be a processor.

The embodiments disclosed herein may be embodied in hardware and ininstructions that are stored in hardware, and may reside, for example,in RAM, flash memory, ROM, Electrically Programmable ROM (EPROM),Electrically Erasable Programmable ROM (EEPROM), registers, a hard disk,a removable disk, a CD-ROM, or any other form of computer-readablemedium known in the art. An exemplary storage medium is coupled to theprocessor such that the processor can read information from, and writeinformation to, the storage medium. In the alternative, the storagemedium may be integral to the processor.

It is also noted that the operational steps described in any of theexemplary embodiments herein are described to provide examples anddiscussion. The operations described may be performed in numerousdifferent sequences other than the illustrated sequences. Furthermore,operations described in a single operational step may actually beperformed in a number of different steps.

Further and as used herein, it is intended that terms “fiber opticcables” and/or “optical fibers” include all types of single mode andmulti-mode light waveguides, including one or more optical fibers thatmay be upcoated, colored, buffered, ribbonized, and/or have otherorganizing or protective structure in a cable such as one or more tubes,strength members, jackets, or the like.

It is to be understood that the description and claims are not to belimited to the specific embodiments disclosed, and that modificationsand other embodiments are intended to be included within the scope ofthe appended claims. Although specific terms are employed herein, theyare used in a generic and descriptive sense only and not for purposes oflimitation.

What is claimed is:
 1. A multiple-input multiple-output (MIMO) remoteunit configured to wirelessly distribute MIMO communications signals towireless client devices in a distributed antenna system, comprising: afirst MIMO transmitter comprising a first MIMO transmitter antennaconfigured to transmit MIMO communications signals in a firstpolarization and a second MIMO transmitter antenna configured totransmit MIMO communications signals in a second polarization differentfrom the first polarization; and a second MIMO transmitter comprising athird MIMO transmitter antenna configured to transmit MIMOcommunications signals in the first polarization and a fourth MIMOtransmitter antenna configured to transmit MIMO communications signalsin the second polarization; the first MIMO transmitter configured to:receive a first downlink MIMO communications signal in a first phaseover a first downlink communications medium, and transmit the firstdownlink MIMO communications signal wirelessly as a first electricaldownlink MIMO communications signal over the first MIMO transmitterantenna in the first polarization; and receive a second downlink MIMOcommunications signal in the first phase over a second downlinkcommunications medium, and transmit the second downlink MIMOcommunications signal wirelessly as a second electrical downlink MIMOcommunications signal over the second MIMO transmitter antenna in thesecond polarization; the second MIMO transmitter configured to: receivea third downlink MIMO communications signal in the first phase over athird downlink communications medium, and transmit the third downlinkMIMO communications signal wirelessly as a third electrical downlinkMIMO communications signal over the third MIMO transmitter antenna inthe first polarization; and receive a fourth downlink MIMOcommunications signal over a fourth downlink communications medium, andtransmit the fourth downlink MIMO communications signal in a secondphase shifted from the first phase, wirelessly as a fourth electricaldownlink MIMO communications signal over the fourth MIMO transmitterantenna in the second polarization.
 2. The MIMO remote unit of claim 1,wherein: the first MIMO transmitter is further configured to transmitthe first and second downlink MIMO communications signals wirelessly toa line-of-sight (LOS) wireless client; and the second MIMO transmitteris configured to transmit the third and fourth downlink MIMOcommunications signals wirelessly to the LOS wireless client.
 3. TheMIMO remote unit of claim 1, further comprising at least one phaseshifter configured to phase shift the fourth downlink MIMOcommunications signal to the second phase.
 4. The MIMO remote unit ofclaim 1, wherein the second MIMO transmitter is configured to receivethe fourth downlink MIMO communications signal in the second phase as aresult of a phase shift of the fourth downlink MIMO communicationssignal in a central unit.
 5. The MIMO remote unit of claim 1, whereinthe second MIMO transmitter is configured to receive the fourth downlinkMIMO communications signal in the second phase as a result of a phaseshift of the fourth downlink MIMO communications signal in the fourthdownlink communications medium.
 6. The MIMO remote unit of claim 1,wherein the third MIMO transmitter antenna is phase offset from thefourth MIMO transmitter antenna by positioning the third MIMOtransmitter antenna in distance from the fourth MIMO transmitterantenna.
 7. The MIMO remote unit of claim 5, wherein the third MIMOtransmitter antenna is phase offset from the fourth MIMO transmitterantenna by the third MIMO transmitter antenna being positioned indistance from the fourth MIMO transmitter antenna.
 8. The MIMO remoteunit of claim 1, wherein the first MIMO transmitter antenna is positionoffset from the second MIMO transmitter antenna by positioning the firstMIMO transmitter antenna in distance from the second MIMO transmitterantenna.
 9. The MIMO remote unit of claim 1, wherein: the first downlinkMIMO communications signal further comprises a first optical downlinkMIMO communications signal; the second downlink MIMO communicationssignal further comprises a second optical downlink MIMO communicationssignal; the third downlink MIMO communications signal further comprisesa third optical downlink MIMO communications signal; and the fourthdownlink MIMO communications signal further comprises a fourth opticaldownlink MIMO communications signal.
 10. The MIMO remote unit of claim9, wherein: the first MIMO transmitter further comprises: a firstoptical-to-electrical (O/E) converter configured to convert the firstoptical downlink MIMO communications signal to the first electricaldownlink MIMO communications signal; and a second O/E converterconfigured to convert the second optical downlink MIMO communicationssignal to the second electrical downlink MIMO communications signal; andthe second MIMO transmitter further comprises: a third O/E converterconfigured to convert the third optical downlink MIMO communicationssignal to the third electrical downlink MIMO communications signal; anda fourth O/E converter configured to convert the fourth optical downlinkMIMO communications signal to the fourth electrical downlink MIMOcommunications signal.
 11. The MIMO remote unit of claim 1, wherein atleast one of the first electrical downlink MIMO communications signal,the second electrical downlink MIMO communications signal, the thirdelectrical downlink MIMO communications signal, and the fourthelectrical downlink MIMO communications signal include a carrierfrequency having an extremely high frequency (EHF) between 30 GHz and300 GHz.
 12. A method of transmitting multiple-input multiple-output(MIMO) communications signals to wireless client devices in adistributed antenna system, comprising: receiving a first downlink MIMOcommunications signal in a first phase over a first downlinkcommunications medium; transmitting the first downlink MIMOcommunications signal wirelessly as a first electrical downlink MIMOcommunications signal over a first MIMO transmitter antenna in a firstpolarization; and receiving a second downlink MIMO communications signalin the first phase over a second downlink communications medium;transmitting the second downlink MIMO communications signal wirelesslyas a second electrical downlink MIMO communications signal over a secondMIMO transmitter antenna in a second polarization; receiving a thirddownlink MIMO communications signal in the first phase over a thirddownlink communications medium; transmitting the third downlink MIMOcommunications signal wirelessly as a third electrical downlink MIMOcommunications signal over a third MIMO transmitter antenna in the firstpolarization; receiving a fourth downlink MIMO communications signalover a fourth downlink communications medium; and transmitting thefourth downlink MIMO communications signal in a second phase shiftedfrom the first phase, wirelessly as a fourth electrical downlink MIMOcommunications signal over a fourth MIMO transmitter antenna in thesecond polarization.
 13. The method of claim 12, further comprising:transmitting the first downlink MIMO communications signal wirelessly toa line-of-sight (LOS) wireless client; transmitting the second downlinkMIMO communications signal wirelessly to the LOS wireless client;transmitting the third downlink MIMO communications signal wirelessly tothe LOS wireless client; and transmitting the fourth downlink MIMOcommunications signal wirelessly to the LOS wireless client.
 14. Themethod of claim 12, further comprising phase shifting the fourthdownlink MIMO communications signal to the second phase.
 15. The methodof claim 14, further comprising receiving the fourth downlink MIMOcommunications signal in the second phase from a central unit that phaseshifts the fourth downlink MIMO communications signal from the firstphase to the second phase.
 16. The method of claim 14, furthercomprising receiving the fourth downlink MIMO communications signal inthe second phase via the fourth downlink communications mediumconfigured to phase shift the fourth downlink MIMO communications signalfrom the first phase to the second phase.
 17. The method of claim 14,comprising phase shifting the fourth downlink MIMO communications signalto the second phase for transmission over the fourth MIMO transmitterantenna.
 18. The method of claim 12, comprising phase offsetting thethird MIMO transmitter antenna from the fourth MIMO transmitter antennaby positioning the third MIMO transmitter antenna in distance from thefourth MIMO transmitter antenna to phase shift the fourth downlink MIMOcommunications signal to the second phase.
 19. The method of claim 12,further comprising position offsetting the first MIMO transmitterantenna from the second MIMO transmitter antenna by positioning thefirst MIMO transmitter antenna in distance from the second MIMOtransmitter antenna.
 20. A distributed antenna system for distributingmultiple-input multiple-output (MIMO) communications signals to wirelessclient devices, comprising: a central unit comprising a central unittransmitter configured to receive a downlink communications signal, andtransmit the received downlink communications signal as a first downlinkMIMO communications signal over a first downlink communications medium,a second downlink MIMO communications signal over a second downlinkcommunications medium, a third downlink MIMO communications signal overa third downlink communications medium, and a fourth downlink MIMOcommunications signal over a fourth downlink communications medium; anda remote unit, comprising: a first MIMO transmitter comprising a firstMIMO transmitter antenna configured to transmit MIMO communicationssignals in a first polarization and a second MIMO transmitter antennaconfigured to transmit MIMO communications signals in a secondpolarization different from the first polarization; a second MIMOtransmitter comprising a third MIMO transmitter antenna configured totransmit MIMO communications signals in the first polarization and afourth MIMO transmitter antenna configured to transmit MIMOcommunications signals in the second polarization; the first MIMOtransmitter configured to: receive the first downlink MIMOcommunications signal in a first phase over the first downlinkcommunications medium, and transmit the first downlink MIMOcommunications signal wirelessly as a first electrical downlink MIMOcommunications signal over the first MIMO transmitter antenna in thefirst polarization; and receive the second downlink MIMO communicationssignal in the first phase over the second downlink communicationsmedium, and transmit the second downlink MIMO communications signalwirelessly as a second electrical downlink MIMO communications signalover the second MIMO transmitter antenna in the second polarization; thesecond MIMO transmitter configured to: receive the third downlink MIMOcommunications signal in the first phase over the third downlinkcommunications medium, and transmit the third downlink MIMOcommunications signal wirelessly as a third electrical downlink MIMOcommunications signal over the third MIMO transmitter antenna in thefirst polarization; and receive the fourth downlink MIMO communicationssignal over the fourth downlink communications medium, and transmit thefourth downlink MIMO communications signal in a second phase shiftedfrom the first phase, wirelessly as a fourth electrical downlink MIMOcommunications signal over the fourth MIMO transmitter antenna in thesecond polarization; and at least one phase shifter configured to phaseshift the fourth downlink MIMO communications signal to the secondphase.
 21. The distributed antenna system of claim 20, wherein: thefirst MIMO transmitter is further configured to transmit the first andsecond downlink MIMO communications signals wirelessly to aline-of-sight (LOS) wireless client; and the second MIMO transmitter isconfigured to transmit the third and fourth downlink MIMO communicationssignals wirelessly to the LOS wireless client.
 22. The distributedantenna system of claim 20, wherein: the central unit further comprisesone or more electrical-to-optical (E/O) converters configured to:convert the first downlink MIMO communications signal into a firstoptical downlink MIMO communications signal, and provide the firstoptical downlink MIMO communications signal to the remote unit over anoptical fiber communications medium; convert the second downlink MIMOcommunications signal into a second optical downlink MIMO communicationssignal, and provide the second optical downlink MIMO communicationssignal to the remote unit over the optical fiber communications medium;convert the third downlink MIMO communications signal into a thirdoptical downlink MIMO communications signal, and provide the thirdoptical downlink MIMO communications signal to the remote unit over theoptical fiber communications medium; and convert the fourth downlinkMIMO communications signal into a fourth optical downlink MIMOcommunications signal, and provide the fourth optical downlink MIMOcommunications signal to the remote unit over the optical fibercommunications medium; and the remote unit further comprises one or moreoptical-to-electrical (O/E) converters configured to: receive the firstoptical downlink MIMO communications signal over the optical fibercommunications medium, and convert the first optical downlink MIMOcommunications signal into the first downlink MIMO communicationssignal; receive the second optical downlink MIMO communications signalover the optical fiber communications medium, and convert the secondoptical downlink MIMO communications signal into the second downlinkMIMO communications signal; receive the third optical downlink MIMOcommunications signal over the optical fiber communications medium, andconvert the third optical downlink MIMO communications signal into thethird downlink MIMO communications signal; and receive the fourthoptical downlink MIMO communications signal over the optical fibercommunications medium, and convert the fourth optical downlink MIMOcommunications signal into the fourth downlink MIMO communicationssignal.
 23. The distributed antenna system of claim 20, wherein thesecond MIMO transmitter is configured to receive the fourth downlinkMIMO communications signal in the second phase as a result of a phaseshift of the fourth downlink MIMO communications signal in a centralunit.
 24. The distributed antenna system of claim 20, wherein the secondMIMO transmitter is configured to receive the fourth downlink MIMOcommunications signal in the second phase as a result of a phase shiftof the fourth downlink MIMO communications signal in the fourth downlinkcommunications medium.
 25. The distributed antenna system of claim 20,wherein the third MIMO transmitter antenna is phase offset from thefourth MIMO transmitter antenna by positioning the third MIMOtransmitter antenna in distance from the fourth MIMO transmitterantenna.
 26. The distributed antenna system of claim 20, wherein thefirst MIMO transmitter antenna is position offset from the second MIMOtransmitter antenna by positioning the first MIMO transmitter antenna indistance from the second MIMO transmitter antenna.
 27. The distributedantenna system of claim 20, wherein at least one of the first electricaldownlink MIMO communications signal, the second electrical downlink MIMOcommunications signal, the third electrical downlink MIMO communicationssignal, and the fourth electrical downlink MIMO communications signalinclude a carrier frequency having an extremely high frequency (EHF)between 30 GHz and 300 GHz.